The present invention relates to optical networking and more particularly to systems and methods for Wavelength Division Multiplexing (WDM) communications.
Impressive strides have been made in the development of WDM communication links. Modern WDM communication links can carry a large number of wavelengths each modulated by a very high data rate signal. Also, the distance over which WDM signals can be transmitted without regeneration by way of optical-electrical-optical conversion has been increased. Furthermore, the distance between purely optical amplification sites along such links has increased.
Telecommunication service providers are, however, also very interested in the economic performance of WDM communication links. Revenue garnered by such links may be low initially and then grow over time as traffic increases. To allow profitable operation even before the maturation of traffic growth, it is desirable to install capacity in stages to the extent that technology allows. Rather than initially installing all of the optical components and systems necessary for a full capacity link immediately it is preferable to set up a modularized architecture where lower cost partial initial deployments are possible.
To support this type of modular installation and upgrade path, it is important to provide an agile optical add-drop multiplexer (OADM) architecture. An OADM adds and/or drops wavelengths of a WDM signal. In the typical traffic growth scenario, the number of added/dropped wavelengths will grow over time. A conventional WDM that fulfills the maximum expected add/drop capacity requirement will be very costly relative to initial revenues.
There are known WDM structures that provide the needed flexibility. Although OADM flexibility postpones certain costs into the future, flexibility itself may also carry a cost due to the types of components that are used. It is thus necessary to find the right trade-off between required flexibility in installation plus upgrade costs.
Flexible OADM structures are known. One type of known flexible OADM structure provides automatic reconfigurability using, e.g., optical switches. This may be referred to as Reconfigurable OADM (R-OADMs). Another type of flexible OADM is manually reconfigurable using e.g., fiber patch-cords and wavelength selective devices. These manually reconfigurable OADMs can be referred to as Flexible OADMs (F-OADMs). Technologies are available currently for implementing both R-OADMs and F-OADMs. For example, it is known to implement an F-OADM using a multiplexer arrayed waveguide grating (AWG) having a number of input ports corresponding to the maximum number of wavelengths to be added and a demultiplexer AWG having a number of output ports corresponding to the maximum number of wavelengths to be dropped.
The flexibility of the known OADM architectures comes at high initial cost and thus does not support the desired business model. Furthermore, many of the current agile architectures suffer from poor optical performance, e.g., high insertion loss on added/dropped wavelengths and/or injection of additional noise on added wavelengths. Existing fixed OADM structures are cost and performance effective only for low counts of channels to be added or dropped and only where traffic reconfiguration or future growth is not an issue. What is needed are OADM structures that provide reconfigurability to accommodate future growth and changes in traffic, that have good optical performance, and that have relatively low initial and upgrade costs.